CN105073788B - Method for low-concentration inverse emulsion polymerization of weakly neutralized polymer and obtained inverse emulsion - Google Patents

Abstract

The present invention relates to a process for preparing polymers by polymerizing an aqueous solution of one or more monomers in a water-in-oil inverse emulsion, wherein one or more of the monomers used contains at least one acid function, the molar percentage of monomers with at least one weak acid function relative to all the monomers used being at least 30%, wherein: i) the polymerization is carried out at a concentration of all monomers in the aqueous solution of from 1.3 to 3.6 mmol per gram of aqueous solution, ii) during the polymerization, not more than 20% of the acid functions present on the monomers with at least one acid function are in neutralized form, and the invention also relates to polymers obtainable by such a process.

Description

Process for low concentration inverse emulsion polymerization of weakly neutralized polymers and obtained inverse lotion

technical field

The present invention relates to the technical field of synthetic polymers comprising weak acid functional groups, generally used as thickeners and/or stabilizers for aqueous media, and more precisely to the manufacture of at least one monomer bearing weak acid functional groups via inverse emulsion polymerization. Processes for obtaining polymers, and also polymers obtainable by such processes.

Background of the invention

Various types of polymers formed from at least one monomer containing weak acid functionality are used as thickeners and/or stabilizers in different types of applications. For example, patents FR 2 810 545 and FR 2 873 126 or patent US 3724 547 may be mentioned. Most often, to obtain the desired thickening and/or stabilizing effect, such polymers are prepared directly as polymers whose acid functions are at least partially neutralized, most often greater than 50%, or even 100%. In fact, it is known from the prior art that synthetic thickeners obtained by inverse emulsion polymerization and from monomers containing acid functional groups, such as acrylic polymers, must be neutralized completely or with a sufficient degree of neutralization before use, For a satisfactory thickening effect. In fact, conversion of acid functional groups to salts can change the state of the polymer and develop the viscosity of the aqueous medium. Patent EP 0 161 038 describes these properties.

When the polymer preparation is carried out directly via water-in-oil inverse emulsion polymerization, for feasibility reasons, as specified in the document US 5 216 070, the desired polymer is composed of at least one monomer containing weak acid functional groups. In the case of the preparation of monomers such as acrylic acid, in order to carry out the polymerization it is necessary to use monomers whose weak acid functions are in neutralized form in order to avoid precipitation problems during the preparation process using inverse emulsions. For example, the publications in US 5 380 465, US 4 539368 and US 4 656 222 and Chinese Chemical Letters, Volume 13, No. 10, Pages 993-996, 2002 all adopt monomers with weak acid functional groups. and percent, or even complete neutralization for inverse emulsion polymerization. This is because, as shown in the prior art, especially in patent US 5 216 070, the preparation of such polymers directly via inverse emulsion polymerization without neutralization of the monomers with weak acid functions used results in Settling/instability problems. In fact, as shown in particular in document US 3 284 393, the preparation of polyacrylic acid latexes via such methods (as described in detail in Example 3) poses stability problems and the latex obtained must be flocculated and concentrated with hydrochloric acid in order to pass through The polymer was obtained by filtration.

Polymers obtained by inverse emulsion polymerization are widely used as rheology modifiers. Thus, there is still a search in this field for polymers exhibiting improved properties in terms of viscosity and thickening and/or stabilizing capacity. For example, patent application WO 2005/097834 provides for the preparation of polymers comprising acid functional groups in the form of inverse emulsions with improved thickening properties. The polymer has a neutralization percentage of 25% to 100%, preferably 30% to 40%.

Summary of the invention

In this context, one of the aims of the Applicant was to develop polymers obtained by inverse emulsion polymerization showing an improved level of thickening performance. The present invention provides a novel method by which this can be achieved.

In the present invention, applicants have focused on the preparation via water-in-oil inverse emulsion polymerization of inverse emulsions of polymers comprising a high molar percentage (relative to all monomers used) of A plurality of weak acid functional monomers, in particular comprises at least 30 mole % of monomers bearing at least one weak acid functional group. The inventors have demonstrated that with such molar percentages of monomers with weak acid functions, the properties of the polymers obtained depend in fact on the one hand on the degree of neutralization of the acid functions of the monomers used during the polymerization, on the other hand Depends on the total concentration of monomers in the aqueous phase. In an original manner compared to the methods proposed in the prior art which recommend polymerization with a high degree of neutralization of the acid functionality, applicants have turned in the present invention to a polymer inverse emulsion polymerization method which exhibits a low neutralization Degree of neutralization, in particular up to 20% of the acid functions present.

In the present invention, applicants provide a process for the preparation of such polymers by polymerizing an aqueous monomer solution in a water-in-oil inverse emulsion, wherein the total monomer concentration ranges from 1.3 mmol to 3.6 mmol per gram of aqueous solution. Polymerization under conditions. Furthermore, applicants have demonstrated that, unlike the higher concentrations used specifically in the prior art, this concentration range is compatible with the low neutralization of polymers obtained with weak acid functionality present and enables the elimination of the prior art Observed stability issues.

In this respect, the invention relates to a process for the preparation of polymers by polymerizing an aqueous solution of one or more monomers in a water-in-oil inverse emulsion, wherein one or more of the monomers used comprises at least one acid function, with The molar percentage of monomers having at least one weak acid function relative to all monomers used is at least 30%, wherein:

i) polymerizing at a concentration of all monomers in the aqueous solution of 1.3 to 3.6 millimoles per gram of aqueous solution,

ii) During the polymerization, a maximum of 20% of the acid functions present on the monomers used having at least one acid function are in neutralized form.

In particular, during the polymerization at most 10%, preferably at most 5% and more preferably at most 2% of the acid functions present on the monomers used having at least one acid function are in neutralized form, whereby even more Favorable thickening properties. According to a particular embodiment, 100% of the acid functions present on the monomers used are in free acid form during the polymerization.

In the present invention, the polymerization is preferably carried out under such conditions that the total monomer concentration present in the aqueous solution is from 1.7 mmol to 3.3 mmol per gram of aqueous solution. In the present invention, the monomer concentration, ie the weight of the monomer contained, is given relative to the total weight of the aqueous solution (also referred to as the aqueous phase).

In particular, it is thus possible to perform this aggregation in the following combinations:

- the concentration of all monomers in the aqueous solution is from 1.3 mmol to 3.6 mmol per gram of aqueous solution and present at most 20%, advantageously at most 10%, preferably at most 5% of the acid functional groups on monomers having at least one acid functional group and more preferably at most 2%, or even 0% in neutralized form,

- the concentration of all monomers in the aqueous solution is from 1.7 mmol to 3.3 mmol per gram of aqueous solution and present at most 20%, advantageously at most 10%, preferably at most 5% of the acid functional groups on monomers having at least one acid functional group And more preferably at most 2%, or even 0% is in neutralized form.

The molar percentage of monomers bearing at least one weak acid function relative to all monomers used is preferably at least 50%, preferably at least 70% and very preferably at least 80%. Such mole percentages can be used with any of the aforementioned monomer concentration/neutralization degree combinations.

In the present invention, it is preferred to carry out the polymerization with monomers having at least one degree of ethylenic unsaturation.

Preferably, the polymerization is carried out with a single monomer bearing at least one weak acid function in a molar percentage of at least 30% relative to all monomers used, the free acid form of which is selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, Crotonic acid, maleic acid and fumaric acid. The monomer bearing at least one weak acid function is very preferably in free acid form or acrylic acid with the degree of neutralization according to the invention. It is also possible to use monomers bearing at least one weak acid function, in particular selected from those listed above, in a total molar percentage of at least 30% relative to all monomers used. Preferably, one of these monomers is acrylic acid in free acid form or with the degree of neutralization according to the invention.

The polymerization can be carried out with at least one monomer bearing at least one strong acid function. In this case it is preferred to carry out the polymerization with a concentration of monomers bearing at least one strong acid function of less than 50% and more preferably less than 30% relative to all monomers used. The polymerization can be carried out, for example, with monomers bearing at least one strong acid function, the free acid form of which is selected from acrylamidoalkylsulfonic acids, such as 2-acrylamido-2-methylpropanesulfonic acid (ATBS). In this case, for example, the polymerization can be carried out with acrylic acid/ATBS or acrylic acid/ATBS/acrylamide combinations, the acid monomer possibly in free acid form, or with a degree of neutralization according to the invention.

Subject matter of the invention is also the polymers obtainable by the process according to the invention, regardless of its implementation variant.

In the present invention, it has been noted that by carrying out the inverse emulsion polymerization by selecting a monomer concentration falling within the range of 1.3 to 3.6 millimoles per gram of aqueous solution, it is possible to prepare An inverse emulsion of an unneutralized acid-functional polymer which is stable, ie no rapid precipitation is observed. Furthermore, it has been demonstrated that such concentration ranges (as opposed to the higher concentrations especially used in the prior art) combined with weak neutralization of the acid functionality present can provide thickening and/or stabilizing efficacy after an at least partial neutralization step polymers that are more effective than prior art polymers obtained by inverse emulsion polymerization.

The term "monomer bearing at least one acid function" means a monomer bearing one or more free or neutralized (ie salified by action of base) acid functions. When a monomer contains more than one acid function, it is possible that it has only a part of the acid function in neutralized form. The acid functionality present may be a weak acid or a strong acid functionality. Typically, the monomers used contain either only weak acid functionality or only strong acid functionality, and most typically monomers with a single acid functionality will be used.

As examples of monomers with at least one weak acid function in free acid form of the -COOH type, mention may be made of acrylic acid, methacrylic acid, itaconic acid and crotonic acid, each containing only one weak acid function, as well as maleic acid and Fumaric acid, which for that matter contains two weak acid functions.

As examples of monomers with strong acid functions in the free acid form, mention may be made of monomers with phosphonic acid or sulfonic acid functions, such as acrylamidoalkylsulfonic acids, such as 2-acrylamido-2-methyl propanesulfonic acid.

In their neutralized form, the acid functions are in anionic form with a counterion or cation depending on the base used for the neutralization, e.g. of the Na ⁺ type when sodium hydroxide is used, or NH when ammonia is used ₄₊ types ^. Historically, the amount of acid functionality in the neutralized form has been controlled by selecting the pH of the aqueous monomer solution, which can be adjusted according to the pKa of the acid functionality present.

The polymerisation may involve a single type of monomer selected from monomers bearing at least one weak acid functionality, or a plurality of monomer types, at least one of which bears at least one weak acid functionality, present on the monomers used and thus The proportion of acid functions present in neutralized form on the copolymer obtained is less than or equal to 20%. In particular, besides the above-mentioned monomers bearing at least one weak acid function, the obtained polymers may contain other monomers, such as monomers bearing at least one strong acid function, neutral (or nonionic) monomers , cationic monomers and/or monomers with hydrophobic properties. In either case, the conditions of aqueous phase formation and polymerization are such that the acid functionality of the monomers involved remains predominantly in the free acid form and is not neutralized by formation of the salified form, or with limited neutralization of less than or equal to 20% degree is weakly neutralized. When less than or equal to 20% neutralization occurs, it is usually carried out in the aqueous phase by adding an appropriate amount of base. Bases such as sodium hydroxide or ammonia can be used.

In particular, the polymerization can be carried out with at least one neutral monomer selected from the group consisting of acrylamide, methacrylamide, N,N-dimethylacrylamide, N-vinylmethyl Acetamide, N-vinylformamide, vinyl acetate, diacetoneacrylamide, N-isopropylacrylamide, N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]acrylamide, (2-Hydroxyethyl)acrylate, (2,3-dihydroxypropyl)acrylate, methyl methacrylate, (2-hydroxyethyl)methacrylate, (2,3-dihydroxypropyl) ) methacrylate, vinylpyrrolidone, or other acrylates, or other ethylenically unsaturated esters. For example, the polymerization can be carried out with 30 to 99 mole % of at least one monomer having one or more weak acid functional groups and 1 to 70 mole % of at least one neutral monomer. The polymerization can be carried out, for example, with an acrylic acid/acrylamide combination, the acrylic acid being in neutral form or having a degree of neutralization according to the invention.

It is also possible to carry out the copolymerization with at least one cationic monomer. As examples of cationic monomers, mention may be made of diallyldialkylammonium salts, such as diallyldimethylammonium chloride (DADMAC); dialkylaminoalkyl acrylates and methacrylates, in particular Acidified or quaternized salts of dialkylaminoethyl acrylates (ADAME) and dialkylaminoethyl methacrylates (MADAME); dialkylaminoalkylacrylamides or methacrylamides such as methyl Acrylamidopropyltrimethylammonium chloride (MAPTAC), acidified or quaternized salts of acrylamidopropyltrimethylammonium chloride (APTAC), and Mannich products such as quaternized di Alkylaminomethacrylamide.

Acidified salts are obtained by methods known to those skilled in the art, in particular by protonation. Quaternized salts are also obtained via methods known in the art, in particular by reaction with benzyl chloride, methyl chloride (MeCl), aryl chloride, alkyl chloride or dimethyl sulfate.

It is also possible to carry out copolymerization with at least one monomer having hydrophobic properties. As examples of monomers with hydrophobic properties, mention may be made of acrylamide undecanoate, methacrylamide dodecanoate and acrylic acid derivatives such as alkyl acrylates or methacrylates, e.g. ethoxylated (25) Behenyl methacrylate.

According to a first variant of the process according to the invention, all monomers bearing at least one acid function used to carry out the polymerization are monomers bearing at least one weak acid function.

According to a second variant of the process according to the invention, the polymerization is carried out with at least one monomer bearing at least one strong acid function in addition to at least one monomer bearing at least one weak acid function. In this case, the molar percentage of monomers bearing at least one strong acid function relative to all monomers used is preferably less than 50%, very preferably less than 30%.

The copolymers obtained by the process according to the invention may in particular consist of a combination of at least one monomer carrying at least one weak acid function and at least one monomer carrying at least one strong acid function, in particular of an acrylic acid/ATBS combination, These acid monomers are in neutral form or have a degree of neutralization according to the invention; it is possible to combine at least one monomer with at least one weak acid function with at least one neutral monomer and optionally at least one monomer with at least A combination of strongly acid-functional monomers, in particular an acrylic acid/acrylamide combination or an acrylic acid/ATBS/acrylamide combination, the acrylic acid and the ATBS being in neutral form or having a degree of neutralization according to the invention; may consist of at least Combination of one monomer with at least one weak acid functionality and at least one cationic monomer and optionally at least one monomer with at least one strong acid functionality; or at least one monomer with at least one weak acid functionality The monomers are formed in combination with at least one neutral monomer and at least one cationic monomer and optionally at least one monomer bearing at least one strong acid functionality.

The monomer was placed in an aqueous solution. The aqueous solution corresponds to the aqueous phase of the inverse emulsion. According to the invention, in the aqueous solution used for the polymerization, at most 20% of the acid functions present on the monomers having at least one acid function are in neutralized form.

The process of the invention is particularly suitable for the preparation of water-soluble or water-swellable polymers.

The term "water-soluble polymer" means a polymer which, when stirred at a concentration of 50 g/l in water at a temperature of 25°C, gives a solution free of insoluble particles.

The term "water-swellable polymer" means a polymer which, when in water at a temperature of 25°C, swells and thickens the solution.

The polymers obtained in the present invention may be linear, structured or crosslinked. The term "structured polymer" means a star-shaped or comb-shaped branched polymer. These branched polymers are generally non-linear polymers with side chains. The term "crosslinked polymer" generally means a non-linear polymer in the form of a three-dimensional network, which is water-insoluble but water-swellable.

When the polymer obtained is branched or crosslinked, it is more particularly branched or crosslinked with monomers comprising two or more ethylenic unsaturations. In order to form branched or crosslinked polymers, at least one monomer which acts as a branching agent is incorporated into the aqueous phase. Such agents are selected, for example, from methylenebisacrylamide (MBA), ethylene glycol diacrylate, polyethylene glycol dimethacrylate, diacrylamide, cyanomethyl acrylate, vinyloxyethyl acrylate, Vinyloxymethacrylate, triallylamine, formaldehyde, glyoxal, glycidyl ethers such as ethylene glycol diglycidyl ether and epoxides, and mixtures thereof.

In the present invention, it should be specified that the total monomer concentration includes monomers acting as branching agents.

The process of the invention is advantageous for the preparation of any structure of linear, structured or crosslinked polymers and is particularly suitable for the preparation of branched or crosslinked polymers.

It is also possible to use transfer agents, also known as chain limiters. The use of transfer agents is particularly advantageous for controlling the molecular weight of the polymer obtained. As examples of transfer agents, mention may be made of methanol, isopropanol, sodium hypophosphite, 2-mercaptoethanol and sodium methallylsulfonate, and mixtures thereof. The amount of branching agent and optionally transfer agent will be adjusted in a known manner by the person skilled in the art, which can be used according to the desire of the person skilled in the art to obtain branched or crosslinked polymers.

In more detail, the method of the present invention comprises the following steps:

a) providing an aqueous solution of the selected monomers, called the aqueous phase,

b) emulsifying said aqueous solution in a water-immiscible phase called the oil phase,

c) performing a polymerization reaction.

Of course, the aqueous solution of step a) has the total concentration of monomers according to the invention, the molar percentage of monomers with at least one weak acid function relative to all monomers used and the acid functions present on the monomers with at least one acid function neutrality.

In order to obtain the desired thickening effect, a neutralization step, also referred to as a post-neutralization step, is most often performed after polymerization, in order to neutralize at least a part, or even all, of the free acid functional groups present on the polymer. In the case of a step in which at least partial neutralization of the free acid functions present in the polymer obtained is carried out after the polymerization reaction, preferably a neutralization of 30% to 100% of all acid functions present on the polymer is obtained percentage.

Thereafter the neutralization step can be carried out in several ways:

- This post-neutralization can be carried out on the inverse emulsion obtained at the end of the process of the invention. This is usually the case when the manufacturer itself neutralizes the polymer in inverse emulsion form.

- The post-neutralization can be carried out on the aqueous solution obtained after inverting the inverse emulsion in water. This is usually the case when the end user uses the inverse emulsion or the powder obtained therefrom in an aqueous solution called a stock solution, which is then added to the medium to be thickened or stabilized. The end user is then free to adjust the polymer concentration, degree of neutralization and nature of the neutralizing agent of the solution.

- The post-neutralization can also be carried out on the composition containing the inverse emulsion or the powder obtained therefrom. Such compositions contain other ingredients depending on the intended application. This is usually the case when the end user uses the inverse emulsion or the powder obtained therefrom directly in the composition to be thickened or stabilized. In the same manner as in the above case, the user can freely adjust the degree of neutralization and the properties of the neutralizing agent.

This neutralization is carried out by a base, the amount and nature of which can be chosen by a person skilled in the art, in a similar manner to the aforementioned neutralization of the monomers.

Typically, the polymerization is carried out in the presence of a water-in-oil emulsifier. The latter are most commonly introduced into the oily phase in which the aqueous solution is emulsified. The term "water-in-oil (W/O) type emulsifier" means an emulsifier whose HLB value is sufficiently low, in particular an HLB value of less than 10, to provide a water-in-oil emulsion.

The HLB value is calculated according to the following relation:

HLB=(% by weight of hydrophilic part)/5

The weight percent of the hydrophilic portion is the ratio of the molecular weight of the hydrophilic portion to the total molecular weight of the molecule.

As examples of such water-in-oil emulsifiers, mention may be made of surfactant polymers such as polyesters with a molecular weight of 1000 to 3000, condensation products between poly(isobutenyl)succinic acid or its anhydrides and polyethylene glycol , block copolymers with a molecular weight of 2500 to 3500, for example under the name Those sold, sorbitan extracts such as sorbitan monooleate, sorbitan isostearate, or sorbitan sesquioleate, certain polyethoxylated Sorbitan esters such as pentaethoxylated sorbitan monooleate or pentaethoxylated sorbitan isostearate, or diethoxylated oleoyl deca Hexaconol or Lauryl Tetraethoxylated Acrylate.

The aqueous solution contains monomers and optionally branching and transfer agents. It may also contain complexing agents such as ethylenediamine or ethylenediaminetetraacetic acid.

Most commonly, the polymerization of step c) is initiated by introducing a free radical initiator into the emulsion formed in step b). As examples of free-radical initiators, mention may be made of redox couples, oxidizing agents being especially cumene hydroperoxide or tert-butylhydroxyperoxide, and reducing agents being especially persulfates such as sodium metabisulfite and mohr's salts. Azo compounds such as 2,2'-azobis(isobutyronitrile) and 2,2'-azobis(2-amidinopropane) hydrochloride can also be used.

Conventionally, the polymerization is usually carried out isothermally, adiabatically or at controlled temperature. That is, the temperature is kept constant, usually between 10 and 50°C (isothermal), or the temperature is allowed to rise naturally (adiabatic), in which case the reaction usually starts at a temperature below 10°C and ends at a temperature usually higher than At 50°C, or finally, the temperature rise was controlled to have a temperature profile between the isothermal and adiabatic curves.

In the process of the invention, it is possible to introduce one or more oil-in-water emulsifiers at the end of the polymerization, preferably at a temperature below 50°C.

The term "emulsifier of the oil-in-water (O/W) type" means an emulsifier whose HLB value is sufficiently high, in particular an HLB value greater than 10, to provide an oil-in-water emulsion. As examples of such oil-in-water emulsifiers, mention may be made of ethoxylated sorbitan esters such as sorbitan oleate ethoxylated (EO20) with 20 equivalents of ethylene oxide, Sorbitan laurate polyethoxylated with 20 moles of ethylene oxide, castor oil polyethoxylated with 40 moles of ethylene oxide, decaethoxylated oleoyl decanol, heptaethoxylated Oxylated lauryl alcohol or sorbitan monostearate polyethoxylated with 20 moles of ethylene oxide.

In the present invention, the emulsifier is introduced in such an amount that the inverse emulsion of the polymer obtained contains usually 1% to 10% by weight, preferably 2.5% to 9% by weight, of a water-in-oil (W/O) type emulsifier , and optionally 2% to 10% by weight, preferably 2.5% to 6% by weight, of an oil-in-water (O/W) type emulsifier.

Typically, the weight ratio of water to oil phase is from 50/50 to 90/10.

The oily phase may consist, for example, of mineral oils, in particular commercially available mineral oils, containing saturated paraffins, saturated isoparaffins, saturated naphthenes or naphthalene-type saturated hydrocarbons with a density of 0.7 to 0.9 at ambient temperature (22° C.); Consisting of vegetable oils; of synthetic oils such as hydrogenated polydecene or hydrogenated polyisobutene; of esters such as octyl stearate or butyl oleate; of vegetable oils such as squalane of vegetable origin; or of several combinations of these oils composition of the mixture.

At the end of the polymerization, it is possible to dilute or concentrate the emulsion obtained. In particular, it is possible to concentrate the emulsion obtained by distillation or to dry it completely to obtain a powder. Such concentration or drying may be performed with or without prior introduction of an emulsifier of the oil-in-water (O/W) type.

A subject of the invention is also a polymer in the form of a water-in-oil inverse emulsion obtained by the process according to the invention, regardless of its implementation variant.

The polymers obtained according to the process of the invention generally require a neutralization step before they are used as thickeners and/or stabilizers. Without an additional neutralization step, in the polymers of the invention at most 20%, preferably at most 10%, even more preferably at most 5%, most preferably at most 2% of the acid functions present are in neutralized form. This low degree of neutralization of the acid functions present provides the user with high flexibility in terms of use, enabling the user to adjust the properties of the polymer at the point of use by subsequently adjusting the degree of neutralization to his desired degree And thereby adjust the desired effect, in particular a thickening and/or stabilizing effect. Such methods also allow the user to select the nature of the neutralizing agent used, compatible with the intended use. The invention also relates to such polymers which are subsequently subjected to a neutralization step to obtain a percentage of neutralized acid functions of 30% to 100% relative to all acid functions present on the polymer.

These polymers thus neutralized provide much better thickening properties, all the rest being the same as the polymers obtained by inverse emulsion polymerization not adhering to the concentration and neutralization conditions defined in the process of the invention. Especially after neutralization, the polymers offer advantageous properties compared to polymers composed of the same monomers but prepared directly by inverse emulsion polymerization at high degrees of neutralization and/or at different total monomer concentrations.

Advantageously, the polymers obtained by the process of the invention are more effective in thickening and/or stabilizing aqueous media after completely neutralizing the free acid functions present, or at least to a greater extent.

The inverse emulsion obtained using the method of the invention can be concentrated, for example by distillation. An inverse emulsion is then obtained whose polymer concentration may be from 30% to 75% by weight, preferably from 40% to 65% by weight.

The polymer obtained from the inverse emulsion of the invention is subsequently subjected to a separation step so as to be in powder form, which is also an integral part of the invention. Such separation steps may be selected, for example, from precipitation, azeotropic distillation and spray drying techniques.

In fact, in the present invention it is possible to concentrate or isolate the polymer in the form of an inverse emulsion obtained directly on leaving the process of the invention without losing the advantageous properties of the polymer obtained. In particular there are various methods of obtaining powders from inverse emulsions of polymers which involve separating the active material from the other constituents of the emulsion, for example:

- Precipitation from a non-solvent medium such as acetone, methanol or any other polar solvent in which the polymer is not soluble. Simple filtration can then separate polymer particles;

- Azeotropic distillation in the presence of an agglomerating agent and a stabilizing polymer enables the production of aggregates which are easily separated by filtration before being subjected to particle drying;

- Spray drying involves creating a cloud of fine droplets of an emulsion in a stream of hot air over a controlled period of time.

Example

I. Example of Preparation of Acrylic Acid/Sodium Acrylate-Based Homopolymer

Example 1:

Add the ingredients of the aqueous phase to a 1 L beaker with magnetic stirring:

-150g of ice-cold acrylic

-605 grams of deionized water

-0.023 g sodium hypophosphite

- 0.10 g of sodium diethylenetriaminepentaacetate

-0.075 g methylenebisacrylamide

- 0.15 g sodium bromate

Next, prepare the organic phase in a 1 L glass reactor with magnetic stirring with the following components:

- 102 g aliphatic hydrocarbon (Isopar L)

- 98 grams white mineral oil (Marcol 152)

-20 g of sorbitan monooleate

- 25 grams of polymeric stabilizer (Hypermer 1083)

The aqueous phase was gradually transferred into the organic phase. The pre-emulsion thus formed was then subjected to strong shear (Ultra Turrax, IKA) for 1 min.

The inverse emulsion was then degassed by simple nitrogen bubbling for 30 minutes.

An aqueous solution containing 1.0% by weight of sodium metabisulfite was then added at a flow rate of 2.5 ml/hour over 1 hour and 30 minutes. Once the maximum temperature was reached, the temperature of the reaction mixture was maintained for 60 minutes before cooling.

Finally, 40 grams of ethoxylated (6 moles) tridecanol were added at about 30°C.

Example 2:

Add the ingredients of the aqueous phase to a 1 L beaker with magnetic stirring:

-175 grams of ice-cold acrylic

-580g deionized water

-0.03 g sodium hypophosphite

- 0.10 g of sodium diethylenetriaminepentaacetate

-0.087 g methylenebisacrylamide

- 0.15 g sodium bromate

Next, the preparation of the organic phase and the remainder of the preparation process were carried out according to Example 1.

Example 3:

Add the ingredients of the aqueous phase to a 1 L beaker with magnetic stirring:

-100g of ice cold acrylic

-655g deionized water

-0.02 g sodium hypophosphite

- 0.10 g of sodium diethylenetriaminepentaacetate

-0.05 g methylenebisacrylamide

-0.15 g sodium bromate

Next, the preparation of the organic phase and the remainder of the preparation process were carried out according to Example 1.

Embodiment 4: neutralize 3.5%/concentration 2.76

The same process as in Example 1 was carried out, adding 5.83 grams of 50% sodium hydroxide solution to the water phase while maintaining the same weight of the water phase by adjusting the amount of deionized water.

Embodiment 5: neutralize 19%/concentration 3.5

Add the ingredients of the aqueous phase to a 1 L beaker with magnetic stirring:

-190g of ice-cold acrylic

-40 grams of 50% sodium hydroxide solution

-525 grams of deionized water

-0.03 g sodium hypophosphite

- 0.10 g of sodium diethylenetriaminepentaacetate

-0.095 g methylenebisacrylamide

- 0.15 g sodium bromate

Next, the preparation of the organic phase and the remainder of the preparation process were carried out according to Example 1.

Comparative example 1:

Add the ingredients of the aqueous phase to a 1 L beaker with magnetic stirring:

-50 grams of ice-cold acrylic

-705 grams of deionized water

-0.01 g sodium hypophosphite

- 0.10 g of sodium diethylenetriaminepentaacetate

-0.043 g methylenebisacrylamide

- 0.15 g sodium bromate

Next, the preparation of the organic phase and the remainder of the preparation process were carried out according to Example 1.

Comparative example 2:

Add the ingredients of the aqueous phase to a 1 L beaker with magnetic stirring:

-199 grams of ice-cold acrylic

- 115 grams of 50% sodium hydroxide solution

-441 grams deionized water

-0.03 g sodium hypophosphite

- 0.10 g of sodium diethylenetriaminepentaacetate

-0.15 g methylenebisacrylamide

- 0.15 g sodium bromate

Next, the preparation of the organic phase and the remainder of the preparation process were carried out according to Example 1.

Comparative example 3:

Add the ingredients of the aqueous phase to a 1 L beaker with magnetic stirring:

-199 grams of ice-cold acrylic

-556 grams of deionized water

-0.03 g sodium hypophosphite

- 0.10 g of sodium diethylenetriaminepentaacetate

-0.1 g methylenebisacrylamide

- 0.15 g sodium bromate

Next, the preparation of the organic phase was carried out according to Example 1.

The aqueous phase was gradually transferred into the organic phase. The pre-emulsion thus formed was then subjected to strong shear (Ultra Turrax, IKA) for 1 min.

The inverse emulsion was then degassed by simple nitrogen bubbling for 30 minutes.

An aqueous solution containing 1.0% by weight of sodium metabisulfite was then added at a flow rate of 2.5 ml/hour. Immediately after the addition of the reducing solution started, the emulsion was destabilized and then coagulated. Polymerization could not proceed and the system was unstable.

Comparative example 4:

Add the ingredients of the aqueous phase to a 1 L beaker with magnetic stirring:

-150g of ice-cold acrylic

-83 grams of 50% sodium hydroxide solution

-522 grams of deionized water

-0.023 g sodium hypophosphite

- 0.10 g of sodium diethylenetriaminepentaacetate

-0.75 g methylenebisacrylamide

- 0.15 g sodium bromate

Next, the preparation of the organic phase and the remainder of the preparation process were carried out according to Example 1.

Polymer Characterization

Procedure : Measure the viscosity of the aqueous polymer solution at an equal concentration [0.16% by weight]

250 g of deionized water was placed in a 400 ml beaker, and then, under mechanical stirring (three blades, 500 rpm), the required amount of inverse emulsion was gradually added to obtain a solution containing 0.16% by weight of active polymer . The pH was then adjusted to 7+/-0.1 with sodium hydroxide. At this pH, 100% of the acid functional groups present on the polymer are neutralized. The solution was allowed to stir for an additional 15 minutes, then allowed to stand for 5 minutes. Viscosity was then measured using a Brookfield RVT viscometer with module 4 and a rotation speed of 20 rpm.

The results are reported in Table 1.

Table 1

ET75 is a commercially available inverse emulsion of acrylic acid homopolymer with 50% of the acid functionality neutralized prior to polymerization.

The polymers obtained by the inverse emulsion polymerization process according to the invention have a much better thickening effect than the polymers obtained by the inverse emulsion process which do not observe the conditions of the invention.

The polymers obtained according to the invention are very effective at very low concentrations.

II. COMPARATIVE STUDY ON THE INVERSE EMULSION PROCESS AND POLYMERS PROPOSED IN THE PRIOR ART

The thickening effect of the polymers obtained by inverse emulsion polymerization as described in the prior art was compared with that of the polymers obtained according to the invention, all other things being equal.

The examples of various prior art documents were repeated, varying only the concentrations and/or percent neutralization to comply with the present invention. Next, using this inverse emulsion, the viscosity was measured following the same protocol as described above.

Hereinafter, AA denotes acrylic acid, AM denotes acrylamide, and ATBS denotes 2-acrylamido-2-methylpropanesulfonic acid.

a. EP 0 161 038

Examples 1A and 1B described on pages 5-6 of patent EP 0 161 038 are repeated. The Examples 1A and 1B were subsequently modified to conform to the present invention.

Example 6

Example 6 corresponds to Example 1A, wherein the amount of acrylamide, acrylic acid and MBA monomers is reduced and replaced by deionized water, so that the same amount of aqueous phase is obtained, and the total monomer concentration of the aqueous phase is 2.8 mmol/ grams, not 4.9.

Example 7

Example 7 corresponds to Example 1A, with the same type of adjustments as in Example 6, in order to obtain a total monomer concentration of the aqueous phase of 3.5 mmol/g instead of 4.9.

Example 8

Example 8 corresponds to Example 1B, with the same type of monomer adjustments as above and additional addition of ammonia to neutralize 20% of the acid functions to obtain a total monomer concentration of 2.8 mmol/g, whereas Not 4.9.

Example 9

Example 9 corresponds to Example 1B, with the same type of adjustments as in Example 8 to obtain a total monomer concentration of 3.5 mmol/g of the aqueous phase instead of 4.9.

The results are reported in Table 2.

Table 2

These examples demonstrate the advantages of combining low monomer concentration and weak neutralization of monomers containing acid functional groups. Such selection can significantly improve the thickening properties obtained.

b.EP 0 503 853

Examples 1, 2 and 7 described on pages 5-6 of patent EP 0 503 853 are repeated. The Examples 1, 2 and 7 were subsequently modified to conform to the present invention.

Example 10

Example 10 corresponds to Example 1, wherein the amount of acrylic acid monomer and NaOH is reduced and deionized water is used instead to obtain the same amount of aqueous phase with a total monomer concentration of 3.4 mmol/g instead of 4.3, and the acid functional group neutralization percentage is 15%, not 100%.

Example 11

Example 11 corresponds to Example 2, wherein the amount of acrylic acid monomer, NaOH and MBA is reduced and replaced by deionized water to obtain the same amount of aqueous phase with a total monomer concentration of 3.4 mmol/g, instead of 4.3, and the percent neutralization of acid functional groups was 15% instead of 100%.

Example 12

Example 12 corresponds to Example 2, wherein the amounts of acrylamide and acrylic acid monomers and MBA and NaOH are reduced and deionized water is used instead to obtain a total monomer concentration of the aqueous phase of 3.4 mmol/g instead of 4.3 , and a percent neutralization of acid functional groups of 15% instead of 100%.

The results are reported in Table 3.

table 3

These experiments also showed the advantages of the method of the present invention compared to the methods of the prior art. Even in the case of linear polymers in which the viscosity remains low (example 1 from EP 0 503 853, as well as example 10), a doubling of the viscosity obtained when using the method of the invention corresponds to the performance level significant improvement.

The combination of the two essential features of the present invention, namely the low concentration of the monomers combined with the low degree of neutralization of the monomers containing the acid functional groups, enables to obtain compounds which provide improved thickening effect with or without the presence of branching agents. polymer.

c. WO 2005/097834

Example 2 described on page 14 of patent WO 2005/097834 is repeated. The percent neutralization and monomer concentration were then reduced to conform to the invention (Example 13).

The results are reported in Table 4.

Table 4

Again, these tests show the advantages of the method of the invention compared to the prior art methods, since it enables a significant improvement in the thickening capacity of the polymers obtained.

d. US 4 677 152

Example 2 of column 8 of patent US 4 677 152 is repeated. The percent neutralization and monomer concentration were then reduced to conform to the invention (Example 14).

The results are reported in Table 5.

table 5

Again, the combination of the two essential features of the present invention, namely the low concentration of monomers in the aqueous phase combined with the low degree of neutralization of the monomers containing acid functional groups, enables to obtain polymers that provide a greater thickening effect.

e.EP 0 645 429

Example 3 on page 5 of patent application EP 0 645 429 is repeated. The percent neutralization was then reduced to conform to the invention (Examples 15 and 16).

The results are reported in Table 6.

Table 6

When using the conditions of the present invention, polymers are obtained with a greatly improved thickening effect.

Claims (35)

1. Process for the preparation of polymers by polymerizing an aqueous solution of one or more monomers in a water-in-oil inverse emulsion, one or more of the monomers used comprising at least one acid function, with at least one weak acid function The molar percentage of monomers relative to all monomers used is at least 30%, wherein: i) polymerizing at a concentration of all monomers in the aqueous solution of 1.3 to 3.6 millimoles per gram of aqueous solution, ii) During the polymerization, at most 20% of the acid functions present on the monomers having at least one acid function are in neutralized form. 2. The method of claim 1, wherein during the polymerisation a maximum of 10% of the acid functions present on the monomers having at least one acid function are in neutralized form. 3. A process as claimed in claim 1 or 2, wherein all acid functional groups present on the monomers are in free acid form during the polymerisation. 4. The method according to claim 1 or 2, wherein the polymerization is carried out under the condition that the concentration of all monomers in the aqueous solution is 1.7 mmol to 3.3 mmol per gram of aqueous solution. 5. A process as claimed in claim 1 or 2, wherein the molar percentage of monomers bearing one or more weak acid functional groups relative to all monomers used bearing acid functional groups is at least 50%. 6. The process as claimed in claim 1 or 2, wherein all monomers used are monomers having at least one ethylenic unsaturation. 7. The method according to claim 1 or 2, wherein the free acid form of the monomer bearing at least one weak acid function is selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid and fumaric acid. 8. The method of claim 1 or 2, wherein the polymerization is carried out with at least one neutral monomer selected from the group consisting of acrylamide, methacrylamide, N,N-dimethylacrylamide Amide, N-vinylmethylacetamide, N-vinylformamide, vinyl acetate, diacetoneacrylamide, N-isopropylacrylamide, N-[2-hydroxy-1,1-bis(hydroxymethyl Base) ethyl] acrylamide, (2-hydroxyethyl) acrylate, (2,3-dihydroxypropyl) acrylate, methyl methacrylate, (2-hydroxyethyl) methacrylate, ( 2,3-dihydroxypropyl)methacrylate and vinylpyrrolidone. 9. The method as claimed in claim 1, wherein all monomers used having at least one acid function are monomers having one or more weak acid functions. 10. A method as claimed in claim 9 wherein the polymerization is carried out with a mixture of acrylic acid/acrylamide monomers and the acid functionality is according to the degree of neutralization indicated in claim 1 , 2 or 3. 11. The method of claim 1, wherein the polymerization is performed with at least one monomer bearing one or more strong acid functional groups. 12. A process as claimed in claim 11, wherein the polymerization is carried out with a molar percentage of monomers bearing one or more strong acid functional groups of less than 50% relative to all monomers used. 13. A process as claimed in claim 11 or 12, wherein the free acid form of the monomer bearing one or more strong acid functional groups is selected from acrylamidoalkylsulfonic acids. 14. The method of claim 10 or 11, wherein a mixture of 2-acrylamido-2-methylpropanesulfonic acid/acrylic acid monomer or 2-acrylamido-2-methylpropanesulfonic acid/acrylic acid The polymerization is carried out with a mixture of acrylamide monomers and acid functional groups according to the degree of neutralization indicated in claim 1, 2 or 3. 15. The method as claimed in claim 1 or 2, wherein the aqueous phase contains at least one monomer acting as a branching agent such that the polymerization results in a crosslinked polymer. 16. The method of claim 15, wherein the branching agent is selected from the group consisting of methylenebisacrylamide (MBA), ethylene glycol diacrylate, polyethylene glycol dimethacrylate, diacrylamide, acrylic acid Cyanomethyl esters, vinyloxyethyl acrylates, vinyloxymethacrylates, triallylamines, formaldehyde, glyoxal, glycidyl ethers, and epoxides, and mixtures thereof. 17. The method of claim 1 or 2, wherein the polymerization is carried out in the presence of a water-in-oil emulsifier. 18. The method of claim 1 or 2, wherein the step of neutralizing at least a portion of the free acid functional groups present on the polymer is performed after polymerization. 19. The method of claim 1 or 2, using a transfer agent selected from the group consisting of methanol, isopropanol, sodium hypophosphite, 2-mercaptoethanol and sodium methallylsulfonate, and its mixture. 20. The method of claim 1, comprising the steps of: a) providing an aqueous solution of the selected monomers, called the aqueous phase, b) emulsifying said aqueous solution in a water-immiscible phase called the oil phase, c) performing a polymerization reaction. 21. The method of claim 20, wherein the weight ratio of the water to the oil phase is 50/50 to 90/10. 22. A process as claimed in claim 20 or 21, wherein the oil phase consists of a mineral oil containing saturated paraffins, saturated isoparaffins, saturated naphthenes or naphthalene-type saturated hydrocarbons having a density of 0.7 to 0.9 at ambient temperature ; consisting of vegetable oils; consisting of synthetic oils; consisting of one or more esters; or consisting of a mixture of several of these oils. 23. A method as claimed in claim 20 or 21, wherein the oil phase contains a water-in-oil emulsifier in which the aqueous solution is emulsified. 24. A method as claimed in claim 20 or 21, wherein the polymerization of step c) is initiated by introducing a free radical initiator into the emulsion formed in step b). 25. The method of claim 1 or 20, wherein, after the polymerisation, one or more oil-in-water emulsifiers are introduced. 26. The method according to claim 1 or 20, wherein, after the polymerization, the obtained emulsion is diluted or concentrated. 27. The method as claimed in claim 1 or 20, wherein after the polymerisation reaction a step of at least partial neutralization of free acid functional groups present in the obtained polymer is carried out. 28. The method of claim 27, wherein the neutralization step results in a percentage of neutralized acid functionality relative to all acid functionality present on the polymer ranging from 30% to 100%. 29. An inverse emulsion containing a polymer obtained by the process according to claim 1 or 20. 30. The inverse emulsion of claim 29, wherein in the polymer at most 20% of the acid functional groups present are in neutralized form. 31. The inverse emulsion of claim 30, wherein the polymer, following a subsequent neutralization step, has a percentage of neutralized acid functionality relative to all acid functionality present on the polymer ranging from 30% to 100%. 32. The inverse emulsion of claim 29 or 30, wherein the polymer is branched or crosslinked. 33. The inverse emulsion of claim 29 or 30, wherein the polymer is in powder form after a subsequent isolation step. 34. The inverse emulsion of claim 33, wherein the separation step is selected from precipitation, azeotropic distillation and spray drying techniques. 35. The inverse emulsion of claim 29 or 30, wherein the polymer is water soluble or water swellable.